Traditional torsional vibration dampers (TVDs) have a single mass-spring system for damping vibrations provided by a strip or ring of elastomer which simultaneously holds the hub and ring of the TVD with respect to each other. Of late, with the advent of Belt Start Generations (BSG) systems, there has been a need for TVDs with inertia rings integral with the hub such that the drive from the crankshaft to the belt is direct (not through the elastomer). However, where high frequencies are required from the TVD, such direct drive TVDs experience three major limitations:
(1) The elastomer compound used for the spring/damper system needs to be very hard. This is achieved by addition of carbon black (binder) that helps to raise the shear modulus of the compound used. However, the addition of carbon black causes two additional problems:                (a) the assembly of the TVD becomes difficult and manufacturing problems such as hi-low elastomer, etc. cause an increase in scrap; and        (b) the damping of the TVD increases to a level that the internal heat generated by the device during operation raises concerns over premature fatigue failure of the spring/damper (elastomer) system.        
(2) The associated moment of inertia of the inertia ring becomes a concern, particularly where a large moment of inertia is desired. The larger the inertia I, the lower the frequency f, based on the equation:f=½π√(kt/I)  (I)where f=natural frequency, kt=torsional stiffness, and I=moment of inertia.
(3) The lack of packaging space available axially for a TVD with a single spring/damper system causes an issue because it limits the width of the elastomer and therefore its torsional stiffness kt based on the equation:
                    kt        =                              π            ⁢                                                  ⁢                          GW              ⁡                              (                                                      Rid                    2                                    ⁢                                      Hod                    2                                                  )                                                          (                                          Rid                2                            -                              Hod                2                                      )                                              (        II        )            where G=shear modulus, W=width of the elastomer, Rid=ring inner diameter, and Hod=hub outer diameter.
The torsional vibration dampers disclosed herein work to alleviate or reduce the potential for these problems by changing the noise, vibration, and harshness (NVH) structure of the problem.